Vehicle headlights are designed to project high intensity beams of light in prescribed patterns to illuminate certain portions of the road in front of the vehicle. Generally, vehicles are equipped with a first pair of headlights for projecting so-called high beams of light to illuminate the entire width of the highway in front of the vehicle. A second pair of headlights projects so-called low beams of light that are directed downwardly and to the right of the high beam so as not to blind an oncoming motorist In some vehicles, high and low beam patterns are projected from the same lamps using different filaments.
In order to produce a desired illumination that maximizes visibility at night without producing excessive glare for oncoming motorists, the headlights must be properly aimed and produce a particular light pattern. Standards for headlight aiming and illumination patterns are prescribed by industrial groups, such as the Society of Automotive Engineers (SAE), and by governmental agencies In general, different aiming and illumination pattern standards have been prescribed for different geographical areas, such as North America and Europe.
Devices and methods for determining proper vehicle headlight aiming during vehicle manufacture and after vehicles have been in use are known. Two examples of known methods and apparatus are described in U.S. Pat. Nos. 3,515,483 to Irwin and 4,435,078 to de Brabander et al. These known devices employ a lens to focus a headlight light beam within a compact electro-optical unit. A number of discrete light intensity sensors are disposed within the optical system for sensing the intensity of light at a relatively small number of positions in the light beam.
In the '483 patent, the intensities of light detected by each of nine discrete light intensity sensors are compared in selected pairs to determine whether established aiming criteria are satisfied within a prescribed degree of accuracy. If the accuracy is not achieved, the position of the headlight is adjusted to achieve the proper aim. This method of comparing the relative intensities of different portions of the light pattern is referred to as the fractional balance method.
The '078 patent employs a variation of the fractional balance aiming technique. There, light intensities measured at about the same number of discrete points by discrete light intensity sensors are used directly in comparison tests, or are multiplied by fractional constants to determine whether a headlight is accurately aimed or not.
Another known method and apparatus for
determining proper headlight aiming is shown in Hopkins, et al, U.S. Pat. No. 4,948,249. The light beam of a headlight is focused on a surface or screen and includes a video sensor for sensing the light intensity in each cell of a continuous matrix of cells that overlies the focused light beam. The video sensor produces an electrical signal, either in digital or analog form, for each cell The signal indicates the cell location and the light intensity in that cell. Analog signals, such as are produced by a charge coupled device, are preferably digitized. The digital signals, i.e. pixels, may be manipulated by a computer to determine headlight aiming accuracy, to correct inaccurate aiming, and to describe the illumination pattern of the headlight.
While the known methods and devices are useful in accurately aiming vehicle headlights, the devices are specifically designed to provide a graphical display of the actual headlight intensity pattern that describes the aim of the headlight being tested. The known devices are not readily adaptable to alternatively display the intensity pattern of a properly aimed headlight with respect to specifications of either the manufacturer or the regulating governmental agency. That is, the known methods and devices are limited in flexibility.
In addition, the known apparatus and methods are inadequate to describe the actual pattern of the light beam on a road surface and the location of exemplary objects that would be visible to the motorist before and after aiming correction In an era of increasing awareness regarding highway safety, it is important that a headlight aiming device provides accurate and rapid results, provides a method that impresses upon motorists the importance of proper headlight aiming, and provides a visual indication of the difference between the actual headlight intensity pattern and a properly aimed headlight intensity pattern.
Accordingly, it is an object of the present invention to provide a vehicle headlight aiming method and apparatus that provides a visual indication of the proper aim of the headlight with respect to applicable specification(s).
Another object of the invention is to provide a headlight aiming method and apparatus that provides a visual comparison between the actual and proper intensity patterns of the light beam on a road surface, and a visual indication of the relative distances the respective intensity patterns would illuminate along the road surface
Still another object of the invention is a method and apparatus for readily measuring headlight intensity patterns.
Yet another object of the invention is the provision of apparatus and methods for measuring both headlight aim accuracy and headlight intensity patterns.
A further object of the invention is a headlight aiming method and apparatus in which errors in headlight aiming are indicated graphically and digitally on a CRT display as a deviation from the proper orientation, and in which correction measures are immediately indicated and observable on the display.
Another object of the invention is the production of a visual display of the intensity pattern of a headlight.